1. Field of the Invention
The present invention relates to an input device used for, for example, a personal computer or a remote control, and a detection device used for, for example, an accelerometer, and particularly to an input device and a detection device (hereinafter typified by an input device) using a resistance type strain sensor element.
2. Description of the Related Art
Various input devices using resistance type strain sensor elements for operation parts or the like are proposed in various industrial fields such as the electrical industry, automotive industry, machine industry, or civil engineering industry.
FIG. 11 is a front view of a conventional input device of this type; FIG. 12 is a bottom view of the input device; FIG. 13 is a detecting circuit diagram of the input device; and FIGS. 14 and 15 are operation explanatory views of the input device.
As shown in FIGS. 11 and 12, the input device of this type is mainly constituted by a thin plate sensor base 1 made of alumina or the like and having slight flexibility, an operation end 2 erectly provided at the center portion of the upper surface of the sensor base 1, and four resistive layers 3a to 3d formed on the lower surface of the sensor base 1 by thick-film printing. As shown in FIG. 12, the four resistive layers 3a to 3d are provided at even intervals horizontally and vertically with a connected portion to the operation end 2 as the center, the resistive layer 3a faces the resistive layer 3c, and the resistive layer 3b faces the resistive layer 3d. These resistive layers 3a to 3d constitute a bridge circuit as shown in FIG. 13. Reference numeral 4 in FIG. 13 designates an X-direction output end; 5, a Y-direction output end; 6, a Z-direction output end; and 7, an external fixed resistor for Z-direction detection.
The relation between a resistance value variation of the resistive layer 3 and a strain amount is generally expressed by the following expression, and the resistance value variation is in proportion to the strain amount:
xcex94R/R=xcex5xc2x7(1+2xcexd)xcex94xcfx81/xcfx81
wherein xcex94R/R is a variation of resistance value; xcex5 is a strain amount; xcexd is a Poisson""s ratio; and xcex94xcfx81/xcfx81 is a variation of specific resistance.
For example, as shown in FIG. 14, in the case where (X-direction) external force F is exerted on the operation end 2 from the left to the right, the sensor base 1 is bent and is deformed as shown in FIG. 14 (for facilitating an understanding, an extremely deformed state beyond an actual state is shown). The resistive layer 3a in the acting direction of the external force F is compressed by this deformation, and its resistance value is lowered, whereas the resistive layer 3c is pulled, and its resistance value is increased. In the case where the external force F is exerted in the direction opposite to the direction shown in FIG. 14, the resistance value of the resistive layer 3a is increased, and the resistance value of the resistive layer 3c is lowered. Incidentally, since the other resistive layers 3b and 3d do not exist in the acting direction of the external force F, their resistance values are not changed.
Although not shown, in the case where the external force F is applied in the Y direction, the resistance values of the resistive layer 3b and the resistive layer 3d are changed, whereas the resistance values of the resistive layer 3a and the resistive layer 3c are not changed. As shown in FIG. 15, in the case where the external force F in the vertical direction (Z direction) is exerted on the operation end 2, the sensor base 1 is bent as shown in FIG. 15, and all the four resistive layers 3a to 3d are pulled by this deformation so that the resistance values are increased.
The changes of the resistance values of the resistive layers 3a to 3d are electrically detected by the detecting circuit of FIG. 13, and a detection signal is obtained from a predetermined output end. Incidentally, with respect to the detection in the vertical direction (Z direction), the total change of the resistance values of the resistive layers 3a to 3d is compared with the external fixed resistor (reference value) 7 for Z direction detection, and a detection signal is obtained.
In the conventional input device, since the detection in the vertical direction is carried out through the comparison between the resistive layer 3 of the variable resistance and the fixed resistance 7, the output in the vertical direction cannot be sufficiently obtained. Besides, the adjustment of detection sensibility in the vertical direction (Z direction) cannot be carried out separately from the adjustment of detection sensibility in the horizontal direction (X and Y directions), and the adjustment of the sensibility in the vertical direction cannot be substantially carried out.
Further, although the detection in the vertical direction is carried out by the resistive layer 3 and the external fixed resistor 7, since the temperature characteristics are different from each other because of a difference in the constitution of both, in order to secure excellent temperature characteristics as a detection device, materials excellent in temperature characteristics must be used for both, and there is a problem that the cost becomes high.
An object of the invention is to solve the defects of the related art and to provide an input device and a detection device in which the output in the vertical direction can be sufficiently obtained, the adjustment of sensibility in the vertical direction can be independently carried out, and the cost can be reduced.
In order to achieve the above object, according to a first aspect of the invention, an input device includes an electrical insulating sensor base which is, for example, a thin plate and is deformable, an operation end connected to a center portion of the sensor base, a first resistive layer (for example, a lower-surface resistive layer) provided on one surface (for example, a lower surface) of the sensor base, a second resistive layer (for example, an upper-surface resistive layer) provided on a surface (for example, an upper surface) opposite to the one surface of the sensor base, and a detecting circuit (for example, a bridge circuit) in which a force is exerted on the operation end in a horizontal direction or a vertical direction to deform the sensor base, and changes of resistance values of the first resistive layer and the second resistive layer by the deformation of the sensor base are electrically detected, wherein the force exerted on the operation end in the horizontal direction is detected by the first resistive layer, and the force exerted on the operation end in the vertical direction is detected by the first resistive layer and the second resistive layer.
According to a second aspect of the invention, in the first aspect, the first resistive layer includes four or more (for example, four) resistive layers provided at even intervals in a circumferential direction of a connected portion, as a center, between the sensor base and the operation end, and the second resistive layer includes one or more (for example, four) resistive layers.
According to a third aspect of the invention, the input device of the first aspect or the second aspect is provided on a keyboard.
According to a fourth aspect of the invention, a detection device includes an electrical insulating sensor base which is, for example, a thin plate and is deformable, a detection end connected to a center portion of the sensor base, a first resistive layer (for example, a lower-surface resistive layer) provided on one surface (for example, a lower surface) of the sensor base, a second resistive layer (for example, an upper-surface resistive layer) provided on a surface (for example, an upper surface) opposite to the one surface of the sensor base, and a detecting circuit (for example, a bridge circuit) in which a force is exerted on the detection end in a horizontal direction or a vertical direction to deform the sensor base, and changes of resistance values of the first resistive layer and the second resistive layer by the deformation of the sensor base are electrically detected, wherein the force exerted on the detection end in the horizontal direction is detected by the first resistive layer, and the force exerted on the detection end in the vertical direction is detected by the first resistive layer and the second resistive layer.
According to a fifth aspect of the invention, in the fourth aspect, the first resistive layer includes four or more (for example, four) resistive layers provided at even intervals in a circumferential direction of a connected portion, as a center, between the sensor base and the detection end, and the second resistive layer includes one or more (for example, four) resistive layers.
In the first aspect and the fourth aspect of the invention, since the first resistive layer and the second resistive layer are provided on the lower surface and the upper surface of the sensor base, that is, the surfaces opposite to each other, when the detection in the vertical direction (Z direction) is carried out, one resistive layer is pulled, and its resistance value is increased the other resistive layer is compressed, and its resistance value is lowered. As stated above, the two resistive layers are variable resistors, and the changes of the resistance values have tendencies opposite to each other, so that a large detection output can be obtained.
Besides, the sensibility adjustment in the vertical direction can be independently carried out through the second resistive layer. Further, since the first resistive layer and the second resistive layer can be formed on the same sensor base by using the same material and by, for example, thick-film printing, the temperature characteristics of the first resistive layer and the second resistive layer can be made identical to each other, and the cost can be reduced.